Pulse or digital communications – Systems using alternating or pulsating current – Plural channels for transmission of a single pulse train
Reexamination Certificate
2000-03-16
2001-11-06
Pham, Chi (Department: 2631)
Pulse or digital communications
Systems using alternating or pulsating current
Plural channels for transmission of a single pulse train
C375S320000
Reexamination Certificate
active
06314141
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the field of a transmitting/receiving system for digital signals transmitted according to the quadrature amplitude modulation (QAM) mode. In particular, the invention provides a method for receiving-end automatic identification of the QAM mode (16-, 64-, 256-QAM; 32-, 128-QAM) of a received signal, the mode having been transmitted in accordance with QAM modulation, in which the received signal is demodulated with symbol values I_Sym and Q_Sym of different significance being obtained. U.S. Pat. No. 5,381,450 and the article titled “Modem Constellation Identification: A Performance Comparison Of Two methods” by Wood et al., 1990 International Conference on Acoustics, Speech and Signal Processing, Vol. 3, 3.-6.04. 1990, pages 1651-1654 have disclosed using statistical evaluation methods in order to identify the QAM mode of a correspondingly transmitted signal at the receiving end. These known methods have to date required a high outlay on circuitry.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for receiving-end automatic identification of a signal at the receiving end, the signal having been transmitted in accordance with the QAM mode, and a circuit for carrying out the method which overcome the above-mentioned disadvantages of the prior art methods and devices of this general type, which method and device can be realized with a relatively low outlay on circuitry.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for receiving-end automatic identification of a quadrature amplitude modulation (QAM) mode of a received signal, the QAM mode being transmitted in accordance with QAM modulation resulting in a transmitted QAM mode, which includes:
demodulating the received signal resulting in symbol values I-Sym and Q-Sym of different significance;
determining the significance of the symbol values I_Sym and Q_Sym; and
adding the symbol values I_Sym and Q_Sym in accordance with their significance for obtaining a statistical distribution of a maxima as a representation of the transmitted QAM mode.
With regard to the method, the object is achieved by virtue of the fact that the significance of the symbol values I_Sym and Q_Sym is acquired, and that the symbol values I_Sym and Q_Sym are added in accordance with their significance in order to obtain a statistical distribution of a maxima as a representation of the transmitted QAM mode.
In accordance with a particularly advantageous development of the method, it is provided that a plurality of symbol values I_Sym and Q_Sym are acquired at the receiving end. The frequency of occurrences of the absolute values I_abs and Q_abs of the symbol values I_Sym and Q_Sym are counted, that the smallest frequency value is defined as a minimum and a largest frequency value is defined as a maximum. A decision level (threshold value) is defined as (maximum+minimum)/2, that the individual frequency values are related to the decision level in order to obtain a bit vector, and that the bit vector is compared with modulation-specific bit masks (reference pattern) in order to identify the QAM mode.
The above-mentioned object is achieved with regard to the circuit for carrying out the method according to the invention, in accordance with the preferred variant evinced above, by virtue of the fact that the below listed components are provided. A first absolute-value forming unit to which the symbol value I_Sym is applied and which serves for generating the absolute value I_abs is provided. A second absolute-value forming unit to which the symbol value Q_Sym is applied and which serves for generating the absolute value Q_abs is provided. A decoder is provided whose inputs are connected to the outputs of the first and second absolute-value forming units in order to generate from the absolute values counting pulses in accordance with the frequency of occurrences of the absolute values. A plurality of counters in accordance with the number of frequencies for the purpose of counting the counting pulses is provided. A buffer store for buffer-storing the counter values of the counters is provided. A device which, in response to a predetermined maximum counter reading being reached by one of the counters, determines the minimum counter reading among the further counters and forms the threshold value (decision level) as (maximum counter reading+minimum counter reading)/2 is provided. A comparator that compares the buffer-stored counter values with the threshold value, and an evaluation device, which compares the comparison results with a reference pattern and outputs a corresponding QAM mode in the event of correspondence with a reference pattern is provided.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for receiving-end automatic identification of a signal at the receiving end, the signal having been transmitted in accordance with the QAM mode, and a circuit for carrying out the method, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
REFERENCES:
patent: 5381450 (1995-01-01), Lane
patent: 5471508 (1995-11-01), Koslov
patent: 5654986 (1997-08-01), Lim
patent: 38 34 377 A1 (1990-04-01), None
patent: 41 02 412 A1 (1992-07-01), None
patent: 195 41 188 C1 (1997-04-01), None
“Modem Constellation Identification: A performance comparison of two methods” (Wood et al.), dated Mar. 4, 1990, pp. 1651-1654.
Köllner Herbert
Solanti Petri
Greenberg Laurence A.
Infineon - Technologies AG
Lerner Herbert L.
Pham Chi
Stemer Werner H.
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